Schottky diode and method of manufacturing the same

ABSTRACT

A Schottky diode comprises: a substrate; a first semiconductor layer located on the substrate; a second semiconductor layer located on the first semiconductor layer, two-dimensional electron gas being formed at an interface between the first semiconductor layer and the second semiconductor layer; a cathode located on the second semiconductor layer and forming an ohmic contact with the second semiconductor layer; a first passivation dielectric layer located on the second semiconductor layer; a field plate groove formed in the first passivation dielectric layer; and an anode covering the field plate groove and a portion of the first passivation dielectric layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international application No.PCT/CN2015/081501 filed on Jun. 15, 2015, which claims the benefit andpriority of Chinese patent application No. 201410663922.0 filed on Nov.19, 2014. Both applications are incorporated herein in their entirety byreference.

TECHNICAL FIELD

The disclosed embodiments relate to semiconductor technology, and moreparticularly to a Schottky diode and a method of manufacturing the same.

BACKGROUND

In the field of high-voltage switches, it is desirable that a diode hasa low reverse leakage current, high reverse voltage and a low forwardturn-on voltage drop. Since power electronic devices based on widebandgap semiconductor materials, particularly gallium nitride materials,have superior characteristics, gallium nitride Schottky diodes have beena hot topic in recent years. Currently, homoepitaxy of gallium nitrideon gallium nitride substrates is still in a small-scale, high-coststage. Although high-quality epitaxial materials and desired deviceperformances can be achieved, such a technology has not been widely useddue to high costs.

At present gallium nitride materials are mainly grown on heterogeneousmaterials, and have relatively high defect densities, e.g., 10⁸ cm',thus desired performances still cannot be obtained for gallium nitrideSchottky diodes having vertical structures. However, High ElectronMobility Devices (HEMTs) based on two-dimensional electron gas channelswhich have high electron mobility in the horizontal direction and areformed by aluminum gallium nitride/gallium nitride heterojunctionstructures have been widely used in the fields of RF and powerelectronics. This is because, on the one hand, gallium nitride is a kindof wide bandgap semiconductor materials which have critical breakdownelectric field intensity about 10 times higher than that of siliconmaterials and thus has a characteristic of high reverse voltage, on theother hand, the two-dimensional electron gas channels can provide verylow turn-on resistances so that power loss of the switching devices canbe reduced. Therefore, horizontal diodes based on aluminum galliumnitride/gallium nitride heterojunction structures gradually become animportant research topic in the industry.

For a Schottky diode formed by direct deposition of Schottky metal on analuminum gallium nitride/gallium nitride heterojunction structure, athickness of an aluminum gallium nitride barrier layer between theSchottky metal and the two-dimensional electron gas usually reaches to20 nm, resulting in a large Schottky barrier thickness. In addition, arelatively large surface state density of the aluminum gallium nitridebarrier layer will lead to the Fermi level pinning effect, which alsoresults in a large Schottky barrier thickness. Therefore, the Schottkydiode has a high forward knee voltage, e.g. greater than 1 V, which isdisadvantageous for reduction of turn-on loss of the diode.

In order to reduce a forward turn-on voltage of the Schottky diode,anode groove structures are proposed. In such structures, an aluminumgallium nitride barrier layer and a portion of a gallium nitride channellayer in an anode region are etched and then deposited with an anodemetal, so that the anode metal at sidewalls and the two-dimensionalelectron gas channel form metal-semiconductor contacts, which eliminatesa Schottky barrier thickness formed by the aluminum gallium nitridebarrier layer with a thickness of 20 nm and reduces the forward kneevoltage, e.g. less than 0.7 V, of the diode. In addition, thetwo-dimensional electron gas channel having high electron mobilityprovides a very low turn-on resistance, so that a Schottky diode withhigh performances such as a low forward turn-on voltage and a lowturn-on resistance can be obtained. Furthermore, the two-dimensionalelectron gas channel has a very low hole concentration due to the widebandgap characteristic of the gallium nitride material, thus the diodehas a very short reverse recovery time. However, the conventionalgallium nitride Schottky diodes still have some shortcomings. Forexample, field-induced thermionic emission or electron tunneling effectin high electric fields will cause an increased reverse leakage current,which reduces the reverse voltage performance of the device.

In order to improve the performances of Schottky diodes, differentstructures have been proposed in some articles and patents.

For example, in the article “Fast Switching GaN Based Lateral powerSchottky Barrier Diode with Low Onset Voltage and Strong ReverseBlocking” (IEEE ELECTRON DEVICE LETTERS, VOL. 33, NO. 3, MARCH 2012) byE. Bahat-Treidel et al., referring to FIG. 1, an anode 11 of a Schottkydiode is designed as a structure of a groove plus a field plate. Themedium under the field plate is a silicon nitride layer 12, metal in thegroove of the anode 11 is directly in contact with two-dimensionalelectron gas 13. In this structure, the reverse voltage performance ofthe Schottky diode can be improved due to the field plate and anincreased distance between the anode and a cathode.

Referring to FIG. 2, a Schottky diode comprising an anode 21 having twolayers of composite dielectric layers is proposed in U.S. Pat. No.8,772,842 B2 entitled “Semiconductor Diodes With Low Reverse BiasCurrents” by Yuvaraj Dora et al. In this structure, the two layers ofcomposite dielectric layers include a layer 21 designed as a field platewith a stepped shape and the other layer 23 as a passivation layer,which reduces a peak electric field intensity and increases a breakdownvoltage.

Referring to FIG. 3, a Schottky diode with a structure having multiplesteps is proposed in U.S. Pat. No. 7,898,004 B2 entitled “SemiconductorHeterostructure Diodes” by Yifeng Wu et al. In this structure, a singledielectric layer is used to form an anode 31 having a stepped fieldplate structure to reduce a peak electric field intensity. Metal in abottom portion of a groove of the anode 31 forms a Schottky contact withsemiconductor material 32, so as to form an anode structure.

In the above-mentioned technical solutions, field plates are added.Under an applied reverse bias voltage, a field plate can reduce areverse leakage current of a Schottky diode by reducing an electricfield intensity at a Schottky junction, and improves a breakdown voltageunder a turn-off state of the Schottky diode. In practice, however, dueto the presence of a passivation dielectric layer under the field plate,a reverse bias voltage applied to an anode will be fully applied to thereverse bias Schottky junction before depleting two-dimensional electrongas in a channel under the anode. In order to achieve an idealpassivation effect and a more optimized electric field mitigation effectby the field plate, the passivation dielectric layer usually has athickness of about 100 nm, which is relatively large compared to analuminum gallium nitride barrier layer which usually has a thickness ofabout 20 nm. In addition, currently silicon nitride which has arelatively small dielectric constant compared to aluminum galliumnitrogen is usually used to form the passivation dielectric layer, arelatively high voltage is required to deplete the two-dimensionalelectron gas. That is, before the two-dimensional electron gas isdepleted and the field plate plays a role in mitigating the electricfield, the Schottky junction has undergone a high reverse bias voltage.In this case, the field-induced thermionic emission and the tunnelingeffect both result in an increased reverse leakage current, thus thereverse leakage current is still at a relatively high level.

Therefore, it is required to further reduce the leakage current under areserve bias state of the gallium nitride Schottky diode and improve thereverse voltage performance thereof.

SUMMARY

In view of this, embodiments of the present invention are directed to aSchottky diode which is capable of reducing a reverse leakage currentand improving a reverse voltage performance. Embodiments of the presentinvention are also directed to a method of manufacturing such a Schottkydiode.

According to one or more embodiments of the present invention, there isprovided a Schottky diode, comprising: a substrate; a firstsemiconductor layer located on the substrate; a second semiconductorlayer located on the first semiconductor layer, two-dimensional electrongas being formed at an interface between the first semiconductor layerand the second semiconductor layer; a cathode located on the secondsemiconductor layer and forming an ohmic contact with the secondsemiconductor layer; a first passivation dielectric layer located on thesecond semiconductor layer; a field plate groove formed in the firstpassivation dielectric layer; and an anode covering the field plategroove and a portion of the first passivation dielectric layer.

In an embodiment, the Schottky diode further comprises an anode grooveformed in the first passivation dielectric layer and the secondsemiconductor layer. The field plate groove is located between the anodegroove and the cathode, the anode covers the anode groove and a portionof the first passivation dielectric layer between the anode groove andthe field plate groove.

In an embodiment, a bottom surface of the anode groove extends to orpasses through a region where the two-dimensional electron gas isformed. A cross-sectional shape of a side surface of the anode groove isany of a straight line, a fold line and an arc or any combinationthereof. An angle between the side surface and a bottom surface of theanode groove is one of a right angle, an obtuse angle and an acuteangle.

In an embodiment, a bottom surface of the field plate groove is locatedwithin the first passivation dielectric layer, or extends to or passesthrough an upper surface of the second semiconductor layer.

In an embodiment, the Schottky diode further comprises a field plategroove dielectric layer located on the first passivation dielectriclayer and the field plate groove.

In an embodiment, the anode extends to the cathode from the field plategroove a distance which is less than a distance between the field plategroove and the cathode.

In an embodiment, the Schottky diode further comprises: a secondpassivation dielectric layer deposited on the anode; and a second anodefield plate deposited on the second passivation dielectric layer. Thesecond anode field plate is electrically connected to the anode.

In an embodiment, the Schottky diode further comprises: a thirdpassivation dielectric layer deposited on the second anode field plate;and a third anode field plate deposited on the third passivationdielectric layer. The third anode field plate is electrically connectedto the anode.

In an embodiment, the second semiconductor layer comprises a firstbarrier layer and a second barrier layer. A blocking layer is furtherdeposited between the first barrier layer and the second barrier layer.The blocking layer is formed of aluminum nitride. The first barrierlayer and the second barrier layer are formed of aluminum galliumnitride. The first barrier layer has an aluminum composition of 10%-15%and a thickness of 5-15 nm. The second barrier layer has an aluminumcomposition of 20%-45% and a thickness of 15-50 nm.

In an embodiment, a cross-sectional shape of a side surface of the fieldplate groove is any of a straight line, a fold line and an arc or anycombination thereof. An angle between the side surface and a bottomsurface of the field plate groove is one of a right angle, an obtuseangle and an acute angle.

In an embodiment, the Schottky diode further comprises at least one of anucleation layer, a buffer layer and a back-barrier layer between thesubstrate and the first semiconductor layer.

According to one or more embodiments of the present invention, there isprovided a method of manufacturing a Schottky diode, comprising:depositing a first semiconductor layer, a second semiconductor layer anda first passivation dielectric layer sequentially on a substrate,two-dimensional electron gas being formed at an interface between thefirst semiconductor layer and the second semiconductor layer; forming acathode on the second semiconductor layer, the cathode forming an ohmiccontact with the second semiconductor layer; forming a field plategroove in the first passivation dielectric layer; and forming an anodecovering the field plate groove and a portion of the first passivationdielectric layer.

In an embodiment, the method further comprises forming an anode groovein the first passivation dielectric layer and the second semiconductorlayer. The field plate groove is located between the anode groove andthe cathode, the anode covers the anode groove and a portion of thefirst passivation dielectric layer between the anode groove and thefield plate groove.

In an embodiment, a bottom surface of the anode groove extends to orpasses through a region where the two-dimensional electron gas isformed.

In an embodiment, the anode groove and the field plate groove are formedby a dry etching process and/or a wet etching process.

In an embodiment, a bottom surface of the field plate groove is locatedwithin the first passivation dielectric layer, or extends to or passesthrough an upper surface of the second semiconductor layer.

According to embodiments of the present invention, by forming the fieldplate groove in the first passivation dielectric layer, a reverseleakage current of a Schottky diode is reduced; meanwhile the advantagesof a low knee voltage and a low turn-on resistance are maintained.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIGS. 1 to 3 are schematic cross-sectional views of Schottky diodesaccording to the prior art;

FIG. 4 is a schematic cross-sectional view of a Schottky diode accordingto a first embodiment of the present invention;

FIGS. 5A and 5B are graphs illustrating the electrical characteristicsof the Schottky diode according to the prior art shown in FIG. 1 andthat of the Schottky diode according to the first embodiment of thepresent invention;

FIGS. 6A and 6B are graphs illustrating the electron concentrationdistribution of the Schottky diode according to the first embodiment ofthe present invention and that of the Schottky diode according to theprior art shown in FIG. 1, respectively, when a same reverse biasvoltage is applied to the anodes;

FIGS. 7A and 7B are graphs illustrating the electric field distributionof the Schottky diode according to the first embodiment of the presentinvention and that of the Schottky diode according to the prior artshown in FIG. 1, respectively, when a same reverse bias voltage isapplied to the anodes;

FIG. 8 is a schematic cross-sectional view of a Schottky diode accordingto a second embodiment of the present invention;

FIG. 9 is a schematic cross-sectional view of a Schottky diode accordingto a third embodiment of the present invention;

FIG. 10 is a schematic cross-sectional view of a Schottky diodeaccording to a fourth embodiment of the present invention;

FIG. 11 is a schematic cross-sectional view of a Schottky diodeaccording to a fifth embodiment of the present invention;

FIG. 12 is a schematic cross-sectional view of a Schottky diodeaccording to a sixth embodiment of the present invention;

FIG. 13 is a schematic cross-sectional view of a Schottky diodeaccording to a seventh embodiment of the present invention;

FIG. 14 is a schematic cross-sectional view of a Schottky diodeaccording to an eighth embodiment of the present invention;

FIG. 15 is a schematic cross-sectional view of a Schottky diodeaccording to a ninth embodiment of the present invention;

FIG. 16 is a schematic cross-sectional view of a Schottky diodeaccording to a tenth embodiment of the present invention;

FIG. 17 is a schematic cross-sectional view of a Schottky diodeaccording to an eleventh embodiment of the present invention;

FIG. 18 is a flowchart of a method for manufacturing a Schottky diodeaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description.

Hereinafter embodiments of the present invention will be described indetail with reference to FIGS. 4 to 18.

FIG. 4 is a schematic cross-sectional view of a Schottky diode accordingto a first embodiment of the present invention. As shown in FIG. 4, theSchottky diode according to the first embodiment of the presentinvention includes a substrate 1 which may be formed of gallium nitride,silicon, sapphire, silicon nitride, aluminum nitride, SOI or othersubstrate material which is suitable for epitaxially growing III-Vnitride.

A nucleation layer 2, a buffer layer 3, a first semiconductor layer 4and a second semiconductor layer 6 are sequentially grown on thesubstrate 1. The nucleation layer 2 may be formed of aluminum nitride orgallium nitride. The buffer layer 3 may be formed of a graded layer ofaluminum gallium nitride or a super-lattice material. The firstsemiconductor layer 4 may be formed of gallium nitride. The secondsemiconductor layer 6 may be formed of aluminum gallium nitride.Two-dimensional electron gas 7 is formed at an interface between thefirst semiconductor layer 4 and the second semiconductor layer 6. Inaddition, the first semiconductor layer 4 has a bandgap width smallerthan that of the second semiconductor layer 6.

Two cathodes 5 are formed on the second semiconductor layer 6. Thecathodes 5 are formed of metal, and form ohmic contacts with the secondsemiconductor layer 6 respectively. It is noted that only one cathode islabeled as 5 in FIG. 4, and the other one is located at the upper leftcorner of FIG. 4. In addition, it is noted that the number of thecathodes 5 is not limited thereto. For example, there may be only onecathode, like the eleventh embodiment which will be described later withreference to FIG. 17.

A first passivation dielectric layer 8 is formed, e.g., deposited, onthe second semiconductor layer 6 and between the cathodes 5. The firstpassivation layer 8 typically uses a silicon nitride dielectric layer ofabout 100 nm. The first passivation dielectric layer 8 serves assuppressing the current collapse effect caused by the surface state ofaluminum gallium nitride. The first passivation dielectric layer 8 maybe formed of any of silicon nitride, silicon dioxide, siliconoxynitride, fluoride and alumina or any combination thereof.

An anode groove 21 is formed in the first passivation dielectric layer 8and the second semiconductor layer 6 and is located between the cathodes5. Two field plate grooves 22 are formed in the first passivationdielectric layer 8 and are located between the anode groove 21 andrespective one of the cathodes 5. It is noted that only one field plategroove is labeled as 22 in FIG. 4, and the other one is located on theother side with respect to the anode groove 21. In addition, it is notedthat the number of the field plate grooves 22 is not limited thereto.For example, there may be only one field plate groove, like the eleventhembodiment which will be described later with reference to FIG. 17.

The anode groove 21 and/or the field plate grooves 22 can bemanufactured by a dry etching process in which different etching speedsare applied in the longitudinal direction and the transverse directionto obtain differently shaped groove structures. Alternatively, the anodegroove 21 and/or the field plate grooves 22 can be manufactured by a wetetching process or other processes. Side surfaces of the anode groove 21and a bottom surface thereof may form right angles, obtuse angles oracute angles or any combination thereof. Similarly, side surfaces of anyone of the field plate grooves 22 and a bottom surface thereof may formright angles, obtuse angles or acute angles or any combination thereof.The specific sizes of the grooves may be determined based on designrequirements. The bottom surface of the anode groove 21 may reach orpass through the two-dimensional electron gas 7 and extend into thefirst semiconductor layer 4. The bottom surfaces of the field plategrooves 22 may reach or exceed an upper surface of the secondsemiconductor layer 6 and extend into the second semiconductor layer 6.

An anode 9 is formed to cover the field plate grooves 22 and a portionof the first passivation dielectric layer 8. For example, referring toFIG. 4, the anode 9 is formed on the anode groove 21, the field plategrooves 22, portions of the first passivation dielectric layer 8 betweenthe anode groove 21 and the field plate grooves 22. In addition, theanode 9 also cover portions of the first passivation dielectric layer 8extending to but not reaching the cathodes 5 from the field plategrooves 22. In other words, one end of the anode 9 extends to anadjacent cathode 5 from an adjacent field plate groove 22 a distancewhich is less than a distance between the field plate groove 22 and thecathode 5. The anode 9 forms Schottky contacts with the secondsemiconductor layer 6, the two-dimensional electron gas 7 and the firstsemiconductor layer 4.

Due to the field plate grooves 22, the field plate metal is close to thetwo-dimensional electron gas 7. Therefore, even under a relatively lowanode reverse bias voltage, the two-dimensional electron gas 7 under thefield plate grooves 22 can be depleted, so as to block current pathsbetween the Schottky junction and the cathodes 5. Accordingly, thereverse bias voltage withstood by the Schottky junction formed by themetal/two-dimensional electron gas is greatly reduced, and the reverseleakage current caused by the field-induced thermionic emission or thetunneling effect is reduced. In this way, the effect of reduction ofleakage current can be achieved.

In addition, since the anode metal in the anode groove 21 directlycontacts the two-dimensional electron gas 7, a barrier height and abarrier width of the Schottky junction can be reduced, therebydecreasing the forward turn-on voltage of the diode.

In practical applications, electrical characteristic parameters, such asforward knee voltage, turn-on resistance, reverse breakdown voltagethreshold and reverse leakage current, will affect the operation of theSchottky diodes. In order to have a good application effect, it isrequired that the Schottky diodes have the characteristics of a lowforward knee voltage, a low turn-on resistance, a high reverse breakdownvoltage threshold and a low reverse leakage current.

FIG. 5A is a graph illustrating the reverse electrical characteristicsof the Schottky diode according to the prior art shown in FIG. 1 withthat of the Schottky diode according to the first embodiment of thepresent invention.

In FIG. 5A, a dashed line a1 represents the reverse electricalcharacteristic of the Schottky diode according to the prior art, while asolid line b1 represents the reverse electrical characteristic of theSchottky diode according to the first embodiment of the presentinvention, where au, an abbreviation of absolute unit, is used as theunit of current represented by the vertical axis. It can be seen fromFIG. 5A that a reverse bias current of the Schottky diode according tothe first embodiment of the present invention is significantly lowerthan that of the Schottky diode according to the prior art under a samereverse bias voltage condition. If the reverse voltage performance ofthe diode is defined by a same leakage current level, it can be seenthat the reverse voltage performance of the Schottky diode having thefield plate grooves proposed by the present invention is remarkablyimproved.

FIG. 5B is a graph illustrating the forward electrical characteristicsof the Schottky diode according to the prior art shown in FIG. 1 withthat of the Schottky diode according to the first embodiment of thepresent invention.

In FIG. 5B, a dashed line a2 represents the forward electricalcharacteristic of the Schottky diode according to the prior art, while asolid line b2 represents the forward electrical characteristic of theSchottky diode according to the first embodiment of the presentinvention, where au, an abbreviation of absolute unit, is used as theunit of current represented by the vertical axis. It can be seen fromFIG. 5B that the relationship between a forward voltage and a forwardcurrent of the Schottky diode according to the first embodiment of thepresent invention is substantially same as that of the Schottky diodeaccording to the prior art. That is, the field plate grooves have littleimpact on the forward electrical characteristics of the Schottky diode.

According to the comparison of the above-mentioned electricalcharacteristics, it is proved that the Schottky diode according to thefirst embodiment of the present invention has the advantage of a lowreverse leakage current, meanwhile maintains the advantages of a lowknee voltage and a low turn-on resistance.

FIGS. 6A and 6B are graphs illustrating the electron concentrationdistribution of the Schottky diode according to the first embodiment ofthe present invention and that of the Schottky diode according to theprior art shown in FIG. 1, respectively, when a same reverse biasvoltage of −20 V is applied to the anodes.

It can be seen from FIGS. 6A and 6B that, when a same reverse biasvoltage of −20 V is applied to the anodes, the electrons in channelregions under the field plate grooves of the Schottky diode according tothe first embodiment of the present invention are substantiallycompletely depleted and the two-dimensional electron gas concentrationis just 2.4×10⁻⁶/cm³, while the electrons in channel regions under theanode field plate of the Schottky diode according to the prior art arenot completely depleted and the two-dimensional electron gasconcentration is as high as 1.7×10¹²/cm³.

FIGS. 7A and 7B are graphs illustrating the electric field distributionof the Schottky diode according to the first embodiment of the presentinvention and that of the Schottky diode according to the prior artshown in FIG. 1, respectively, when a same reverse bias voltage isapplied to the anodes.

It can be seen from FIGS. 7A and 7B, when a same reverse bias voltage isapplied to the anodes, the electric field intensity at side surfaces ofthe anode groove of the Schottky diode according to the prior art is3.1×10⁶ V/cm, while the electric field intensity at side surfaces of theanode groove of the Schottky diode according to the first embodiment ofthe present invention is 2.6×10⁶ V/cm, which is about 83% of that in theprior art. In the Schottky junction, the reverse leakage current causedby field-induced thermionic emission or the tunneling effect has anexponential correlation with the electric field intensity. Therefore,the reverse leakage current can be effectively reduced in the firstembodiment of the present invention.

Through comparison of the channel electron concentration shown in FIGS.6A and 6B and comparison of the electric field intensity shown in FIGS.7A and 7B, it is further proved that in the anode structure of theSchottky diode according to the first embodiment of the presentinvention, the two-dimensional electron gas in channel regions under thefield plate grooves can be depleted even under a low reverse biasvoltage, so that the electric field intensity withstood by the Schottkyjunction formed by metal/two-dimensional electron gas is reduced.

FIG. 8 is a schematic cross-sectional view of a Schottky diode accordingto a second embodiment of the present invention. The duplicateddescription on the same or similar elements as those in the firstembodiment will not be repeated.

As shown in FIG. 8, different from the first embodiment, two field plategrooves 22 a of the Schottky diode according to the second embodimentextend into, but not beyond, the second semiconductor layer 6. Adistance between a bottom surface of any one of the field plate groves22 a and the two-dimensional electron gas 7 in a height direction shouldbe greater than 5 nm to ensure a concentration sufficient for thetwo-dimensional electron gas 7 to operate normally. In contrast, if theabove-mentioned distance is less than 5 nm, it is possible that thetwo-dimensional electron gas 7 will be depleted completely, which willincrease the forward turn-on voltage of the diode.

Compared with the Schottky diode according to the first embodiment ofthe present invention, the field plate metal of the Schottky diodeaccording to the second embodiment is closer to the two-dimensionalelectron gas 7. Therefore, the two-dimensional electron gas 7 under thefield plate grooves 22 a can be depleted under a lower anode reversebias voltage. Accordingly, the reverse bias voltage withstood by theSchottky junction formed by the metal/two-dimensional electron gas isfurther reduced, and the reverse leakage current of the Schottkyjunction is further reduced.

FIG. 9 is a schematic cross-sectional view of a Schottky diode accordingto a third embodiment of the present invention. The duplicateddescription on the same or similar elements as those in the firstembodiment will not be repeated.

As shown in FIG. 9, different from the first embodiment, the Schottkydiode according to the third embodiment of the present invention furthercomprises a field plate groove dielectric layer 10 located on thepassivation dielectric layer 8 and the field plate grooves 22.

In this embodiment, the field plate groove dielectric layer 10 may beformed of any one of silicon nitride, silicon dioxide, siliconoxynitride and aluminum oxide or any combination thereof

Compared with the Schottky diode according to the first embodiment ofthe present invention, the field plate groove dielectric layer 10 isfurther included between the field plate grooves 22 and the anode 9.Therefore, at a reverse bias voltage, the leakage current flowingthrough the Schottky junction with the field plate groove structure canbe further reduced.

FIG. 10 is a schematic cross-sectional view of a Schottky diodeaccording to a fourth embodiment of the present invention. Theduplicated description on the same or similar elements as those in thefirst embodiment will not be repeated.

As shown in FIG. 10, different from the first embodiment, thepassivation dielectric layer 8 is not etched completely when field plategrooves 22 b are formed, so that the remained part of the passivationdielectric layer 8 in the height direction forms a field plate groovelayer. This can be realized by utilizing dry etching process andcontrolling the etching time. Therefore, the field plate grooves 22 bhave fewer depths compared with the field plate grooves 22 of theSchottky diode according to the first embodiment. That is, a bottomsurface of any of the field plate grooves 22 b does not reach the secondsemiconductor layer 6, instead it is located inside the firstpassivation dielectric layer 8.

Compared with the Schottky diode according to the third embodiment ofthe present invention, in this embodiment, the process of depositingdielectric materials for the field plate grooves 22 b is simplified.

FIG. 11 is a schematic cross-sectional view of a Schottky diodeaccording to a fifth embodiment of the present invention. The duplicateddescription on the same or similar elements as those in the firstembodiment will not be repeated.

As shown in FIG. 11, different from the first embodiment, in theSchottky diode according to the fifth embodiment of the presentinvention, a back-barrier layer 11 is inserted under the firstsemiconductor layer 4.

The back-barrier layer 11 may be formed of aluminum gallium nitride withan aluminum composition of 5%-15%. And the aluminum composition of theback-barrier layer 11 is lower than that of the second semiconductorlayer 6.

Since aluminum gallium nitride has a larger bandgap width than galliumnitride, the introduction of the back-barrier layer 11 can provide abetter restriction on the two-dimensional electron gas channel in thefirst semiconductor layer 4. Under application of an external reversebias voltage, electrons will be leaked to the cathodes 5 from the anode9 through the buffer layer 3, thereby increasing the reverse leakagecurrent of the Schottky diode. The introduction of the aluminum galliumnitride back-barrier layer 11 with low aluminum composition will hinderthe electrons to enter the buffer layer 3, so as to reduce the reverseleakage current leaked through the buffer layer 3.

Compared with the Schottky diode according to the first embodiment ofthe present invention, in this embodiment, the back-barrier layer 11with low aluminum composition is further included, thus the reverseleakage current flowing through the buffer layer 3 is reduced.

FIG. 12 is a schematic cross-sectional view of a Schottky diodeaccording to a sixth embodiment of the present invention. The duplicateddescription on the same or similar elements as those in the firstembodiment will not be repeated.

As shown in FIG. 12, different from the first embodiment, a secondsemiconductor layer of the Schottky diode according to this embodimentcomprises a first barrier layer 6 a and a second barrier layer 6 b.

The first barrier layer 6 a may be formed of aluminum gallium nitridewith an aluminum composition of 10%-15%, and have a thickness of 5-15nm. The second barrier layer 6 b may be formed of aluminum galliumnitride and have a thickness of 15-50 nm. The second barrier layer 6 bhas an aluminum composition of 25%-45% which is higher than that of thefirst barrier layer 6 a.

The field plate grooves 22 are formed in the first passivationdielectric layer 8 and the second barrier layer 6 b having a highaluminum composition by the field plate groove etching process. Thebottom surfaces of the field plate grooves 22 may reach or pass throughan upper surface of the first barrier layer 6 a. Since portions of thefirst barrier layer 6 a under the field plate grooves 22 have lowaluminum concentrations and small thicknesses, the two-dimensionalelectron gas 7 under the field plate grooves 22 has lower concentrationcompared with the first embodiment, and is easier to be depleted whenthe anode is applied with a negative bias voltage. Accordingly, thereverse bias voltage withstood by the Schottky junction formed by themetal/two-dimensional electron gas is further reduced, and the reverseleakage current caused by the field-induced thermionic emission or thetunneling effect is further reduced.

In addition, portions of the second barrier layer 6 b between the fieldplate grooves 22 and the cathodes 5 have high aluminum composition,which makes the two-dimensional electron gas 7 thereunder have arelatively high concentration, thereby allowing the Schottky diodeaccording to this embodiment to have a relatively low turn-on resistanceand reducing the forward turning-on voltage of the diode.

Furthermore, in this embodiment, a back-barrier layer (not shown) may befurther inserted under the first semiconductor layer 4 to suppress thereverse leakage current flowing through the buffer layer 3. Theback-barrier layer may be formed of aluminum gallium nitrogen. Since theback-barrier layer further depletes the two-dimensional electron gas 7,the turn-on resistance becomes high and the forward turning-on voltageis increased. Therefore, it is necessary to limit the aluminumcomposition of the aluminum gallium nitrogen of the back-barrier layerto 5%-8%, i.e., less than the aluminum composition of the first barrierlayer 6 a. In this way, it is ensured that the two-dimensional electrongas 7 under the field plate grooves 22 still has a certain concentrationand is not completely depleted, so that the forward turning-on voltageof the Schottky diode remains low.

FIG. 13 is a schematic cross-sectional view of a Schottky diodeaccording to a seventh embodiment of the present invention. Theduplicated description on the same or similar elements as those in thesixth embodiment will not be repeated.

As shown in FIG. 13, different from the sixth embodiment, the Schottkydiode according to the seventh embodiment of the present inventionfurther comprises a blocking layer 6 c located between the first barrierlayer 6 a and the second barrier layer 6 b. The blocking layer 6 c maybe formed of aluminum nitride.

Compared with the Schottky diode according to the sixth embodiment ofthe present invention, in this embodiment, the blocking layer 6 c isfurther inserted between the first barrier layer 6 a and the secondbarrier layer 6 b. With the introduction of the aluminum nitrideblocking layer, an etching selection ratio between aluminum nitride andaluminum gallium nitride is relatively large during dry etching, so thatsurfaces of the grooves can be stopped at exact positions during theetching process, which improves the uniformity of the knee voltage ofthe Schottky diode.

FIG. 14 is a schematic cross-sectional view of a Schottky diodeaccording to an eighth embodiment of the present invention. Theduplicated description on the same or similar elements as those in thefirst embodiment will not be repeated.

As shown in FIG. 14, different from the first embodiment, the Schottkydiode according to the eighth embodiment of the present inventionfurther comprises a second passivation dielectric layer 12 deposited onthe anode 9 and a second anode field plate 13 deposited on the secondpassivation dielectric layer 12. The second anode field plate 13 isinterconnected with the anode 9.

In this embodiment, the second passivation dielectric layer 12 may beformed of any of silicon nitride, silicon dioxide, silicon oxynitrideand aluminum oxide or any combination thereof

Compared with the Schottky diode according to the first embodiment ofthe present invention, in this embodiment, the second passivationdielectric layer 12 is deposited on the anode 9, and the second anodefield plate 13 which is interconnected with the anode 9 is deposited onthe second passivation dielectric layer 12. With the addition of thesecond anode field plate 13, a peak electric field at edges of the anode9 between the anode 9 and the cathodes 5 is further reduced, and reversevoltage performance of the diode is improved.

FIG. 15 is a schematic cross-sectional view of a Schottky diodeaccording to a ninth embodiment of the present invention. The duplicateddescription on the same or similar elements as those in the eighthembodiment will not be repeated.

As shown in FIG. 15, different from the eighth embodiment, the Schottkydiode according to the ninth embodiment of the present invention furthercomprises a third passivation dielectric layer 14 deposited on thesecond passivation dielectric layer 12 and the second anode field plate13, as well as a third anode field plate 15 deposited on the thirdpassivation dielectric layer 14. The third anode field plate 15 isinterconnected with the anode 9 and the second anode field plate 13.

In this embodiment, the third passivation dielectric layer 14 may beformed of any of silicon nitride, silicon dioxide, silicon oxynitrideand aluminum oxide or any combination thereof.

Compared with the Schottky diode according to the eighth embodiment ofthe present invention, in this embodiment, the third passivationdielectric layer 14 and the third anode field plate 15 are deposited onthe second passivation dielectric layer 12 and the second anode fieldplate 13, and the third anode field plate 13 is interconnected with theanode 9. With the addition of the third anode field plate 15, the peakelectric field at the edges of the anode 9 between the anode 9 and thecathodes 5 is further reduced, and reverse voltage performance of thediode is further improved.

FIG. 16 is a schematic cross-sectional view of a Schottky diodeaccording to a tenth embodiment of the present invention. The duplicateddescription on the same or similar elements as those in the firstembodiment will not be repeated.

As shown in FIG. 16, different from the first embodiment, in theSchottky diode according to the tenth embodiment of the presentinvention, the first semiconductor layer 4 is deposited on an uppersurface of the second semiconductor layer 6, the cathodes 5 and surfacesof the first semiconductor layer 4 form ohmic contacts, and the anode 9and the surfaces of the first semiconductor layer 4 form a Schottkycontact.

Since the first semiconductor layer 4 has a bandgap width smaller thanthat of the second semiconductor layer 6, the first semiconductor layer4 and the cathodes 5 are more likely to form ohmic contacts. Similar tothe Schottky diode according to the first embodiment of the presentinvention, in this embodiment, electrical characteristics of low reverseleakage current and low forward knee voltage can be realized as well.

FIG. 17 is a schematic cross-sectional view of a Schottky diodeaccording to an eleventh embodiment of the present invention. Theduplicated description on the same or similar elements as those in thefirst embodiment will not be repeated.

As shown in FIG. 17, different from the first embodiment, in theSchottky diode according to the eleventh embodiment of the presentinvention, there is only one cathode 5 and one field plate groove 22.

Similar to the Schottky diode according to the first embodiment of thepresent invention, in this embodiment, electrical characteristics of lowreverse leakage current and low forward knee voltage can be realized aswell. Furthermore, the manufacturing process of the diode is more simplecompared with that according to the first embodiment.

FIG. 18 is a flowchart of a method for manufacturing a Schottky diodeaccording to an embodiment of the present invention. As shown in FIG.18, the method comprises the following steps:

Step S1: forming, e.g. depositing, a first semiconductor layer, a secondsemiconductor layer and a first passivation dielectric layersequentially on a substrate, two-dimensional electron gas being formedat an interface between the first semiconductor layer and the secondsemiconductor layer;

Step S2: forming a cathode on the second semiconductor layer, thecathode forming an ohmic contact with the second semiconductor layer;

Step S3: forming a field plate groove in the first passivationdielectric layer; and

Step S4: forming an anode covering the field plate groove and a portionof the first passivation dielectric layer.

The method may further comprise forming an anode groove in the firstpassivation dielectric layer and the second semiconductor layer. In thiscase, the field plate groove is located between the anode groove and thecathode, the anode covers the anode groove and a portion of the firstpassivation dielectric layer between the anode groove and the fieldplate groove. A bottom surface of the anode groove extends to or passesthrough a region where the two-dimensional electron gas is formed. Abottom surface of the field plate groove is located within the firstpassivation dielectric layer, or extends to or passes through an uppersurface of the second semiconductor layer.

Furthermore, the anode groove and/or the field plate groove can beformed by a dry etching process and/or a wet etching process.

It will be understood that the embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments of the present invention have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thepresent invention as defined by the following claims and theirequivalents.

What is claimed is:
 1. A Schottky diode, comprising: a substrate; afirst semiconductor layer located on the substrate; a secondsemiconductor layer located on the first semiconductor layer,two-dimensional electron gas being formed at an interface between thefirst semiconductor layer and the second semiconductor layer; a cathodelocated on the second semiconductor layer and forming an ohmic contactwith the second semiconductor layer; a first passivation dielectriclayer located on the second semiconductor layer; a field plate grooveformed in the first passivation dielectric layer; and an anode coveringthe field plate groove and a portion of the first passivation dielectriclayer.
 2. The Schottky diode of claim 1, further comprising: an anodegroove formed in the first passivation dielectric layer and the secondsemiconductor layer, wherein the field plate groove is located betweenthe anode groove and the cathode, the anode covers the anode groove anda portion of the first passivation dielectric layer between the anodegroove and the field plate groove.
 3. The Schottky diode of claim 2,wherein a bottom surface of the anode groove extends to or passesthrough a region where the two-dimensional electron gas is formed. 4.The Schottky diode of claim 2, wherein a cross-sectional shape of a sidesurface of the anode groove is any of a straight line, a fold line andan arc or any combination thereof, an angle between the side surface anda bottom surface of the anode groove is one of a right angle, an obtuseangle and an acute angle.
 5. The Schottky diode of claim 1, wherein abottom surface of the field plate groove is located within the firstpassivation dielectric layer, or extends to or passes through an uppersurface of the second semiconductor layer.
 6. The Schottky diode ofclaim 1, further comprising: a field plate groove dielectric layerlocated on the first passivation dielectric layer and the field plategroove.
 7. The Schottky diode of claim 1, wherein the anode extends tothe cathode from the field plate groove a distance which is less than adistance between the field plate groove and the cathode.
 8. The Schottkydiode of claim 1, further comprising: a second passivation dielectriclayer deposited on the anode; and a second anode field plate depositedon the second passivation dielectric layer, wherein the second anodefield plate is electrically connected to the anode.
 9. The Schottkydiode of claim 8, further comprising: a third passivation dielectriclayer deposited on the second anode field plate; and a third anode fieldplate deposited on the third passivation dielectric layer, wherein thethird anode field plate is electrically connected to the anode.
 10. TheSchottky diode of claim 1, wherein the second semiconductor layercomprises a first barrier layer and a second barrier layer.
 11. TheSchottky diode of claim 10, further comprising a blocking layerdeposited between the first barrier layer and the second barrier layer.12. The Schottky diode of claim 11, wherein the blocking layer is formedof aluminum nitride.
 13. The Schottky diode of claim 10, wherein thefirst barrier layer and the second barrier layer are formed of aluminumgallium nitride, the first barrier layer has an aluminum composition of10%-15% and a thickness of 5-15 nm, the second barrier layer has analuminum composition of 20%-45% and a thickness of 15-50 nm.
 14. TheSchottky diode of claim 1, wherein a cross-sectional shape of a sidesurface of the field plate groove is any of a straight line, a fold lineand an arc or any combination thereof, an angle between the side surfaceand a bottom surface of the field plate groove is one of a right angle,an obtuse angle and an acute angle.
 15. The Schottky diode of claim 1,further comprising at least one of a nucleation layer, a buffer layerand a back-barrier layer between the substrate and the firstsemiconductor layer.
 16. A method of manufacturing a Schottky diode,comprising: forming a first semiconductor layer, a second semiconductorlayer and a first passivation dielectric layer sequentially on asubstrate, two-dimensional electron gas being formed at an interfacebetween the first semiconductor layer and the second semiconductorlayer; forming a cathode on the second semiconductor layer, the cathodeforming an ohmic contact with the second semiconductor layer; forming afield plate groove in the first passivation dielectric layer; andforming an anode covering the field plate groove and a portion of thefirst passivation dielectric layer.
 17. The method of claim 16, furthercomprising forming an anode groove in the first passivation dielectriclayer and the second semiconductor layer, wherein the field plate grooveis located between the anode groove and the cathode, the anode coversthe anode groove and a portion of the first passivation dielectric layerbetween the anode groove and the field plate groove.
 18. The method ofclaim 17, wherein a bottom surface of the anode groove extends to orpasses through a region where the two-dimensional electron gas isformed.
 19. The method of claim 17, wherein the anode groove and thefield plate groove are formed by a dry etching process and/or a wetetching process.
 20. The method of claim 16, wherein a bottom surface ofthe field plate groove is located within the first passivationdielectric layer, or extends to or passes through an upper surface ofthe second semiconductor layer.